Abstract: The effect of ovarian fluid in activating solution on per cent motility and motility duration was examined, using Rainbow trouts Oncorhynchus mykiss W., 1792. Proportion of motile sperm decreased in ovarian fluid concentrations increased from 1.8 to 2.6 %. Motility duration generally decreased as the concentration of ovarian fluid increased from 0.2 to 2.6. Thus, the motility duration was related to the ovarian fluid concentration in activating solution. These results indicates that the presence of ovarian fluid in activating solution decreased the motility duration and the presence of a high concentration of ovarian fluid in activating solution, ovarian fluid is considered important for decreasing motility in Rainbow trout sperm.